1. Field of the Invention
The present invention generally relates to explosive initiators and more particularly to a new type of initiator which is activated through the use of a focused beam of light.
2. Prior Art
Most explosive initiators are in the form of a cartridge having a generally cylindrical shape, and having threads on the explosive output end, a flange near the middle of the initiator with some type of wrenching configuration and some means for introducing initiation energy into the input end of the initiator opposite from the output end. In the case of an optical initiator, light energy is typically supplied through an optical fiber that is terminated with a standard type of fiber-optic connector that mates with the input end of the initiator cartridge.
A sealed optical initiator cartridge must have a transparent window that allows light energy to pass through it while still providing the necessary sealing function to protect the cartridge contents, including the explosive therein, against environmental degradation and in some cases contain the products of reaction in the cartridge following the initiation. The window of a typical initiator is merely a flat piece of glass and has no focusing effect on the light passing through it. Thus, light continues to spread out in a cone configuration from the moment it leaves the output end of the optical fiber, as it passes through the window and until it impinges on the explosive behind the window. This requires a higher light energy output than with a focused beam of light because the unfocused beam spreads the light out over a greater area and is absorbed by a greater quantity of material to be initiated.
Standard fiber-optic connectors are typically 1.2 inches long and are usually used with a strain relief boot attached thereto which adds another 1 inch in length. Moreover, most optical fiber cannot be bent to a smaller radius than about 1 inch. As a result, a typical optical explosive initiator with a typical connector and optical fiber attached require about 3 inches of clearance above the surface on which the initiator cartridge is typically mounted. In addition, even if such clearance is available, the resulting rigid mounting of the fiber end can cause excessive bending stress in the fiber, when the fiber is subjected to forces perpendicular or in other directions from the main axis of the cartridge.
Accordingly, there remains a need for an improved explosive initiator which permits light emitted from an optical fiber end to turn through an angle, preferably a right angle so as to permit the clearance required above the mounting surface for the initiator cartridge to be reduced from about 3 inches to as little as about 0.5 inch, while still using standard fiber optic connector components. It would also be desireable if the initiator permitted the connector and fiber end to rotate freely around the cartridge axis so as to increase mounting flexibility and reduce bending stress on the optical fiber. Further, it would be desireable if the light from the fiber could be focused in the initiator so as reduce the light energy required to initiate the explosive reaction.